JPH034491B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a glass for a fluoride optical fiber, which is used for producing an infrared-transmissive fluoride optical fiber, and has a reduced concentration of OH groups, which causes impurity absorption loss.

Conventional glass for fluoride optical fibers is made by adding an appropriate amount of NH ₄ F/HF to a predetermined amount of fluoride raw material mixed.
Simply melt the mixture in a platinum crucible or gold crucible in an inert gas atmosphere, or sinter and melt in an active gas atmosphere such as HF or _CCl4 , and then mold the melt. It was produced by casting. mixed
The amount of NH ₄ F・HF is limited, and since the glass raw materials are sintered at temperatures above 239.5°C, which is the boiling point of NH ₄ F・HF, they scatter quickly, so the OH group removal effect is small and Only a small portion of the OH groups are removed. Furthermore, in the method of simply melting in an active gas, the raw materials are vaporized and the composition of the glass is shifted, so the melting process cannot be carried out for a long time, and therefore the OH removal effect cannot be improved. Furthermore, after the raw material is melted, the reaction between the atmospheric gas and the OH groups mainly occurs only on the surface of the melt, and the efficiency of removing OH groups is extremely low. For this reason, the amount of residual OH groups in the glass melt is large, so the amount of impurity absorption loss due to OH groups in the optical fiber produced by drawing the preform produced by annealing the obtained fluoride optical fiber glass has become high, and its transmission loss characteristics have become significantly worse.

In the present invention, in order to remove OH group impurities in the production of fluoride optical fiber glass, HF, F ₂ , CF ₄ , BF ₃ , Cl ₂ ,
It is characterized by removing OH groups by reacting CCl ₄ or SOCl ₂ , and its purpose is to produce a glass for fluoride optical fibers having an extremely low OH group concentration.

The glass raw materials used in the present invention include Li, Na,
Bi, Mg, Ca, Sr, Ba, Al, Sn, Pb, Sb, Bi,
These are fluorides such as Zn, Y, Gd, La, Gd, Lu, Th, Zr, and Hf.

The gases used for the OH group removal reaction include HF, F ₂ , CF ₄ ,
There are gases such as BF ₃ , Cl ₂ , CCl ₄ , SOCl _{2 ,} etc., or a mixture of these gases diluted with an inert gas. In addition, the crucible used for the vitrification reaction is made of platinum or gold,
A raw material pretreatment crucible that has holes on a part or the entire surface of the bottom of the crucible and a pipe for guiding the gas to the raw material, and collecting the glass melt that has fallen from the holes in the bottom of the pretreatment crucible, which is also made of platinum or gold. It consists of a melting crucible. The vitrification reaction and casting into a mold for producing an optical fiber preform are performed in a dry box purged with nitrogen, etc., and the inner wall is protected by a material that is not easily attacked by fluorine, such as fluororesin. It is desirable that the reaction be carried out while preventing water and oxygen from entering the reaction system.

In the production method according to the present invention, a fluoride glass raw material is placed in a pretreatment crucible, placed on a melting crucible, placed in an electric furnace, and heated at 300°C to 550°C.
For 0.5 to 5 hours, a gas such as HF is introduced through a pipe installed in the pretreatment crucible, jetted out below the bottom of the pretreatment crucible, and diffused into the glass raw material through a hole drilled at the bottom of the crucible. of
When the reaction between OH groups and gases such as HF is promoted, and then the temperature of the electric furnace is raised to 800℃ to 1000℃, the glass raw material begins to melt and is placed under the pretreatment crucible through the hole at the bottom of the crucible. After being dropped into a melting crucible and stored and melted at the above temperature for 1 to 3 hours, in order to produce an optical fiber preform,
The preform is casted into a mold preheated at a temperature of 200°C to 300°C in the same dry atmosphere and slowly cooled to room temperature.

The present invention will be explained in detail by carrying out the following,
The present invention is not limited in any way by this.

Example 1 FIG. 1 is a schematic diagram showing an example of the configuration of an apparatus used in the manufacturing method of the present invention.

In FIG. 1, 1 is a platinum electric furnace, 2 is a platinum crucible for pretreatment, 3 is a lid with an exhaust hole for the platinum crucible for pretreatment, 4 is a platinum pipe, 5 is a supporter that holds down the platinum pipe 4, and 6 is a supporter for holding down the platinum pipe 4. Platinum crucible for melting, 7
8 is a vertically movable crucible stand on which platinum crucible 6 is placed.
1 is a stage on which the platinum crucible 2 is placed, 9 is an electric furnace stand, 10 is a raw material, and 11 is a hole at the bottom of the platinum crucible 2. In FIG. 2, 12 is a quartz glass mold annealing cylinder, 13 is a three-part brass mold with a circular diameter of 9 mmφ and an internal length of 150 mm, the entire surface of which has been "gold plated", and 14 is an electric furnace for annealing.

The glass melting furnace and mold annealing furnace shown in FIG. 1 and FIG. 2, which will be described later, are installed in a glove box, and the inside of the glove box is replaced with nitrogen to create a dry atmosphere. Fluoride glass raw materials ZrF ₄ , BaF ₂ ,
GdF ₃ and AlF ₃ are placed in platinum crucible 2, and 2 is placed on stage 8. Next, while holding down the pipe 4 with the supporter 5, the lid 3 is placed on the platinum crucible 2, and the pipe of the lid 3 is connected to the exhaust system. Platinum crucible 6 is placed on crucible stand 7 lowered below the electric furnace, crucible stand 7 is lifted into the electric furnace, and platinum crucible 6 is inserted into platinum crucible 2. Therefore, the platinum electric furnace 1 was set at 450° C., and OH group removal treatment was performed for 3 hours while flowing HF gas through the supporter 4 at a rate of 0.5 min. After 3 hours, the platinum electric furnace 1 was heated to 900° C. and melted for 1 hour. During this time, all the raw materials are transferred to the platinum crucible 6 through the hole 11 made at the bottom of the platinum crucible 2.
It flowed inside.

FIG. 2 is a schematic diagram showing an example of the configuration of an annealing apparatus used for producing a preform for optical fiber, in which a mold 13 is placed in a mold annealing tube 12, and an annealing electric The furnace 14 was set at 260°C to preheat the tube 12. After 2 hours, the HF that had been flowing was stopped, the crucible stand 7 was lowered, the platinum crucible 6 was taken out, and the glass melt was casted into the preheated mold 13.
After annealing at 260° C. for 20 hours in the tube 12, it was slowly cooled to room temperature to obtain a fluoride glass preform with an outer diameter of 9 mmφ and a length of 140 mm.

Application Example The preform obtained in Example 1 was drawn by the method shown in FIG. The transparent fluoride optical fiber preform 15 is inserted into the fluororesin tube 16, and the small electric furnace 18 placed on the electric furnace table 17 is placed.
The fluoride optical fiber 20 was wound onto the winding bobbin 19 by raising the air at a rate of 0.1 cm/min. A fluororesin-coated graded index type optical fiber (outer diameter 500 μm, cladding diameter
200 μm) was obtained. This optical fiber had a window of 100 dB/Km or less in the 2.5 μm band, and was capable of infrared transmission with absorption loss due to OH groups reduced to 800 dB/Km or less in the 2.9 μm band. The absorption loss due to OH groups remained over 10,000 dB/Km with the conventional method, but with the method of the present invention, it has been reduced to one-tenth of the conventional method.
We were able to reduce it to below.

As explained above, according to the present invention, HF can be efficiently diffused into the fluoride glass raw material, and since the glass melting and casting are performed in a dry atmosphere, the fluoride can be produced with very little OH group contamination. It has the advantage of being able to produce preforms for optical fibers.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the configuration of an apparatus used in the manufacturing method of the present invention, FIG. 2 is a schematic diagram showing an example of the configuration of an annealing apparatus used for manufacturing an optical fiber preform, and FIG. 1 is a schematic diagram of drawing the base material obtained in Example 1 of the present invention. 1...Platinum electric furnace, 2...Platinum crucible for pretreatment, 3...Lid with exhaust pipe for the platinum crucible for pretreatment, 4...Platinum pipe, 5...Supporter,
6... Platinum crucible for melting, 7... Crucible stand, 8...
...Stage, 9...Electric furnace stand, 10...Raw material, 1
1... Hole, 12... Quartz glass mold annealing tube, 13... Brass mold, 14... Electric furnace for annealing, 15... Preform, 16... Fluorine resin tube, 17... Electric furnace stand, 18... Small electric furnace, 19... Winding bobbin, 20... Fluoride optical fiber.

Claims (1)

[Claims] 1 Fluoride glass raw materials are converted into HF, F ₂ , BF ₃ , CF ₄ , Cl ₂ , CCl ₄ in a fine powder state without sintering.
Alternatively, after being pretreated with SOCl ₂ , it is melted in an electric furnace and the glass melt is poured out to synthesize a glass with an extremely low amount of OH groups. Method.